The present invention relates to sampling downhole fluids in a wellbore penetrating a subterranean formation. In particular, this invention relates to techniques for collecting downhole fluid samples and retrieving the samples to a surface location.
Wellbores, which are also known as boreholes, are drilled for hydrocarbon prospecting and production. It is often desirable to perform various evaluations of the formations penetrated by a wellbore during drilling operations, such as during periods when actual drilling has temporarily stopped. In some cases, the drill string may be provided with one or more drilling tools to test and/or sample the surrounding formation. In other cases, the drill string may be removed from the wellbore, in a sequence called a “trip,” and a wireline tool may be deployed into the wellbore to test and/or sample the formation. The samples or tests performed by such downhole tools may be used, for example, to locate valuable hydrocarbon-producing formations and manage the production of hydrocarbons therefrom.
Such drilling tools and wireline tools, as well as other wellbore tools conveyed on coiled tubing, drill pipe, casing or other conveyors, are also referred to herein simply as “downhole tools.” Such downhole tools may themselves include a plurality of integrated modules, each for performing a separate function, and a downhole tool may be employed alone or in combination with other downhole tools in a downhole tool string.
More particularly, formation evaluation often requires that fluid from the formation be drawn into a downhole tool, or module thereof, for testing in situ and/or sampling. Various devices, such as probes and/or packers, are extended from the downhole tool to isolate a region of the wellbore wall, and thereby establish fluid communication with the formation surrounding the wellbore. Fluid may then be drawn into the downhole tool using the probe and/or packers.
A typical probe employs a body that is extendable from the downhole tool and carries a packer at an outer end thereof for positioning against a sidewall of the wellbore. Such packers are typically configured with one relatively large element that can be deformed easily to contact the uneven wellbore wall (in the case of open hole evaluation), yet retain strength and sufficient integrity to withstand the anticipated differential pressures. These packers may be set in open holes or cased holes. They may be run into the wellbore on various downhole tools.
Another device used to form a seal with the wellbore sidewall is referred to as a dual packer. With a dual packer, two elastomeric rings are radially expanded about a downhole tool to isolate a portion of the wellbore wall therebetween. The rings from a seal with the wellbore wall and permit fluid to be drawn into the downhole tool via the isolated portion of the wellbore.
The mudcake lining the wellbore is often useful in assisting the probe and/or dual packers in making the appropriate seal with the wellbore wall. Once the seal is made, fluid from the formation is drawn into the downhole tool through an inlet therein by lowering the pressure in the downhole tool. Examples of probes and/or packers used in various downhole tools are described in U.S. Pat. Nos. 6,301,959, 4,860,581, 4,936,139, 6,585,045, 6,609,568, and 6,719,049, and U.S. Patent Application Publication No. 2004/0000433, which are incorporated herein by reference.
Fluid is drawn into the down tool through an inlet in the probes or packers. Fluid flows into a flowline and is selectively delivered to a sample chamber or bottle for collection therein. Examples of sample chambers and related techniques used in downhole tools are depicted in U.S. Pat. Nos. 6,745,835, 6,688,390, 6,659,177, 5,803,186, 5,233,866, 5,303,775, and 5,377,755, among others. Sample chambers are containers typically provided with an internal piston that retains the collected fluid under pressure. Once fluid is collected in the sample chamber, the tool is retrieved to the surface, and the sample chambers are removed for further analysis. In some cases, the sample chambers are removed at the surface for evaluation. In other cases, the sample chambers are taken to an offsite facility for further testing.
Despite the advances in sampling technology, there remains a need to obtain samples without interrupting the downhole operations being performed by the downhole tool. In some instances, sample chambers may become defective, full or other wise inoperable during operations. These remains a need for techniques for obtaining samples more quickly and/or without having to remove the tool. In such cases, it is desirable to retrieve one or more sample chambers from the downhole tool without withdrawing the tool.
Techniques have been developed for retrieving, measurement and logging while drilling tools (MWD, LWD) from downhole drilling tools. These MWD and LWD tools are typically deployed into and retrieved from downhole drilling tools via wireline or slickline devices. In such cases, the component is sent downhole through a mud channel extending through the downhole drilling tool and operatively inserted into the bottom hole assembly of the downhole drilling tool. Examples of such devices and related techniques are described in U.S. Pat. No. 6,577,244. However, no known techniques exist for retrieving sample chambers from downhole devices or tools. Difficulty exists in maintaining samples under the desired pressure, and preventing contamination of the sample during extraction and/or transport.
A need therefore exists for a system and method capable of collecting a sample and transporting it to the surface without requiring the removal of the downhole tool. It is desirable that such a system be operable even under harsh drilling environments, such as offset drilling conditions. It is further desirable that such a system be capable of isolating the sample from contamination and/or damage during transportation to the surface. These and other features of the invention are set forth herein.